Chapter 5: Programming Practices - TOC - 5.9 ERRONEOUS EXECUTION AND BOUNDED ERRORS

5.9.9 Protected Objects

guideline

Do not invoke a potentially blocking operation within a protected entry, a protected procedure, or a protected function.

rationale

The Ada Reference Manual (1995, §9.5.1) lists the potentially blocking operations:

- Select statement

- Accept statement

- Entry-call statement

- Delay statement

- Abort statement

- Task creation or activation

- External call on a protected subprogram (or an external requeue) with the same target object as that of the protected action

- Call on a subprogram whose body contains a potentially blocking operation

Invoking any of these potentially blocking operations could lead either to a bounded error being detected or to a deadlock situation. In the case of bounded error, the exception Program_Error is raised. In addition, avoid calling routines within a protected entry, procedure, or function that could directly or indirectly invoke operating system primitives or similar operations that can cause blocking that is not visible to the Ada run-time system.